Pd-catalyzed desulfitative and denitrogenative Suzuki-type reaction of arylsulfonyl hydrazides

Article abstract of DOI:10.1039/c5ra01363a

A palladium-catalyzed desulfitative-denitrogenative coupling of arylsulfonyl hydrazides and arylboronic acids with the assistance of catalytic ligands is described. The reaction showed very good selectivity and tolerated a wide range of functionalities without the aid of expensive copper- or silver-based stoichiometric co-oxidants. We have successfully applied this new cross-coupling reaction to the synthesis of terphenyls and OTBN.

Full text of DOI:10.1039/c5ra01363a

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Pd-catalyzed desulfitative and denitrogenative
Suzuki-type reaction of arylsulfonyl hydrazides†
Cite this: RSC Adv., 2015, 5, 27029
*
Shuangling Zhong, Chenggang Sun, Sen Dou and Wencong Liu
Received 23rd January 2015
Accepted 11th March 2015
DOI: 10.1039/c5ra01363a
www.rsc.org/advances
A
palladium-catalyzed desulfitative–denitrogenative coupling of species.7 Aer arylsulfonyl chlorides have been engaged in Pd-
arylsulfonyl hydrazides and arylboronic acids with the assistance of catalyzed Suzuki cross-coupling for a while, the sodium arene-
catalytic ligands is described. The reaction showed very good selec- sulnates have been demonstrated as good electrophilic partners
tivity and tolerated a wide range of functionalities without the aid of in Suzuki-type coupling reactions by Qi et al.,8 for its nature of a
expensive copper- or silver-based stoichiometric co-oxidants. We much milder arene source into the aryl syntheses than aryl
have successfully applied this new cross-coupling reaction to the carboxylic acids reagents (Scheme 1, desultation). In addition,
synthesis of terphenyls and OTBN.
Pd-catalyzed Suzuki cross-coupling through the cleavage of C–N
bond providing another alternative for electrophilic partners
(Scheme 1, denitrogenation). The arenediazonium salts have
been applied as electrophilic reagents in Suzuki-type coupling
along with the release of N2 under mild conditions for a long
time.9 In 2014, the rst example of Pd-catalyzed Suzuki cross-
coupling of readily available arylhydrazines with arylboronic
acids via C–N bond cleavage was developed under air by Gao and
co-workers.10 It provided a new procedure through the activation
of C–N bond to form biaryl skeleton. Another attractive manner
for Suzuki coupling reaction could be start up via both deni-
trogenation and desultation under mild conditions. Arylsul-
fonyl hydrazides are readily accessible solids and compatible
with moisture, and they have been widely employed to the
synthesis of hydrazones, reductants and heterocycles.11 Arylsul-
fonyl hydrazides are stable in air and can be easily prepared in
one step from arylsulfonyl chlorides and hydrazine hydrates.
More signicantly, they could both serve as ideal sulfonylating or
Pd-catalyzed cross-coupling reactions are among the most
powerful methods in organic synthesis.1 Such procedures
involving the coupling of activated electrophilic partners with
nucleophilic organoboron donors are well known as Suzuki-
type cross-couplings.2 Today, the Suzuki reaction is the most
widely employed of the cross-coupling reactions, nding
continual application in the synthesis of drug-like molecules in
the pharmaceutical industry.
Traditionally, aryl halides are most widely used electrophilic
reagents in Pd-catalyzed chemistry. The Suzuki cross-coupling
reactions with aryl iodines, aryl bromides, even aryl chlorides,
have been well documented (Scheme 1, dehalorination).3
Subsequently, the methods utilizing aryl tosylates/mesylates
which derived from the respective phenols in Suzuki–Miyaura
coupling have been developed. The transformation proceeded
via C–O bond cleavage instead of C–X bond (Scheme 1, deoxi-
dation).4 Much attention has been paid to decarboxylative cross-
coupling reactions. Such reactions use stable carboxylic acids as
substrates and give access to various valuable product through
the removal of CO2.5 The rst decarboxylative coupling reaction
of aryl carboxylic acids with arylboronic acids has been reported
by Liu and co-workers (Scheme 1, decarboxylation).6
Nowadays, the cleavage of C–S bond has been emerged as an
attractive alternative to trigger the formation of organometallic
College of Resources and Environment, Jilin Agricultural University, Changchun
130118, P. R. China. E-mail: dou_sen@126.com; Fax: +86-431-84510969; Tel: +86-
431-84532851
Scheme 1 Outline of Pd-catalyzed Suzuki-type coupling of various
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c5ra01363a
coupling partners with arylboronic acids.
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thiolating agents by means of denitrogenation,12 and serve as isolated with Pd(OAc)2 (Table 2, entry 1). Applications of PdCl2
arylating reagents by means of desultation.13 Herein, we wish to afforded 77% yield of 4-methyl biphenyl (Table 2, entry 2). Other
report a palladium-catalyzed desultative and denitrogenative Pd(II) catalyst such as PdBr2 and PdI2 did not favor the forma-
Suzuki-type reaction of arylsulfonyl hydrazides with arylboronic tion of the product (Table 2, entries 3 and 4). Pd(TFA)2 is effi-
acids without additional oxidants, with the assistance of ligands ciently and selectively catalyst which afforded the desired
and bases under aerobic conditions for 6 hours, forming a novel product in the yield of 92% (Table 2, entry 5). Pd(0) catalysts
strategy for biaryl synthesis (Scheme 1, this work).
such as Pd(PPh3)4 and Pd2(dba)3 inhibit the formation of biaryls
In our preliminary optimization of the reaction conditions, 4- (Table 2, entries 6 and 7). During the screening of solvents, we
methylbenzenesulfonohydrazide and phenylboronic acid were found that ether solvents had a dramatic effect on the reaction
chosen as the model substrates with Pd(OAc)2 in the presence of compared to many regular solvents, such as toluene, CH3CN,
K2CO3 in MTBE (methyl tert-butyl ether), the desired products DMSO, DMF and NMP (N-methyl-pyrrolidone) (Table 2, entries
were detected in the yield of 45% (Table 1, entry 1). To our delight, 8–12). The yields of the products are obtained with THF, 1,4-
the introduction of ligand was helpful to improve the efficiency of dioxane, DME (1,2-dimethoxyethane) and DIPE (diisopropyl
this transformation. We began to screen ligands for the assis- ether) in 71–84% (Table 2, entries 13–16), and MTBE was shown
tance of the Pd-catalyzed system. Many ligands have been tested the best.
and showed obvious inuence on the reaction. Table 1 presents
With the optimized reaction conditions in hand, we inves-
the effects of various ligands for the Pd-catalyzed Suzuki-type tigated the effect of electronic and structural variations of the
coupling reaction. Examination of entries 2 and 3 of Table 1 desulnative–denitrogenative coupling. The scope of the reac-
shows that the cross-coupling yields were increased to 63% and tion is presented in Table 3. Generally, the reaction efficiency
61% respectively, by the addition of 10 mol% of dppe (1,2-bis(- was not sensitive to the electronic property of the groups on the
diphenylphosphino)ethane) and dppp (1,3-bis(diphenylphos- phenyl ring of boronic acids. Electron-donating groups
phino)propane) as the ligand. Much higher yields for the desired (methoxy substituent) gave a slight lower yield than electron-
product were obtained by the addition of phosphine ligands such withdrawing groups (nitro substituent) (Table 3, entries 3a
as BINAP ((ꢀ)-2,20-bis(diphenylphosphino)-1,10-binaphthalene), and 3b). The hindrance of the phenyl ring of boronic acids had
JohnPhos (2-(di-t-butylphosphino)biphenyl) SPhos (2-dicyclohex- slight effect on the efficiency (Table 3, entries 3b–3d). Halogen
ylphosphino-20,60-dimethoxybiphenyl) and XPhos (2-dicyclohex- substituents such as uoro, chloro, and bromo were tolerated
ylphosphino-20,40,60-triisopropylbiphenyl) (Table 1, entries 4–7). under the optimal reaction conditions, and the desired prod-
Interestingly, even higher cross-coupling yields were isolated by ucts were obtained in good yields (Table 3, entries 3e–3g).
the addition of dppb (1,2-bis(diphenylphosphino)butene), dppf
(1,10-bis(dicyclohexylphosphino)ferrocene) and Xantphos (4,5-
bis(diphenylphosphino)-9,9-dimethylxanthene), leading to the
formation of 1,4-diphenylbuta-1,3-diyne at yields of 88%, 91%
and 95%, respectively (Table 1, entries 8–10). N-contained ligands
such as TMEDA (N,N,N,N-tetramethylethylenediamine), DBU (1,8-
diazabicyclo[5.4.0]undec-7-ene), DBN (1,5-diazabicyclo[4.3.0]non-
5-ene) and DABCO (1,4-diazabicyclo[2.2.2]octane), were ineffi-
cient (Table 1, entries 11–14).
Table 2 Catalyst and solvent selection for Pd-catalyzed desulfitative–
denitrogenative Suzuki-type couplinga
Aerwards, we optimized catalysts using in this desulna-
tive–denitrogenative reaction with Xantphos and K2CO3 at 60 ꢁC
in MTBE for 6 h under air. 95% yield of the desired product was
Entry
Catalyst
Solvent
Yieldb (%)
1
2
3
4
5
6
7
8
Pd(OAc)2
PdCl2
PdBr2
MTBE
MTBE
MTBE
MTBE
MTBE
MTBE
MTBE
Toluene
CH3CN
DMSO
DMF
NMP
THF
1,4-Dioxane
DME
DIPE
95
77
82
76
92
12
16
—
—
20
17
28
71
77
80
84
PdI2
Pd(TFA)2
Pd2(dba)3
Pd(PPh3)4
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Table 1 Suzuki-type-coupling reaction in the presence of various
ligandsa
Entry
Ligand
Yieldb (%)
Entry
Ligand
Yieldb (%)
9
1
2
3
4
5
6
7
—
dppe
dppp
BINAP
JohnPhos
SPhos
XPhos
45
63
61
75
82
79
80
8
9
dppb
dppf
Xantphos
DABCO
TMEDA
DBU
88
91
95
44
51
49
41
10
11
12
13
14
15
16
10
11
12
13
14
DBN
a
a
Reaction conditions: 4-methylbenzenesulfonohydrazide (0.5 mmol),
Reaction conditions: 4-methylbenzenesulfonohydrazide (0.5 mmol),
phenylboronic acid (0.5 mmol), Pd(OAc)2 (5.0 mol%), ligand (10 phenylboronic acid (0.5 mmol), catalyst (5.0 mol%), Xantphos (10
mol%), K2CO3 (0.5 mmol), MTBE (1.0 ml) at 60 ꢁC for 6 hours under mol%), K2CO3 (0.5 mmol), solvent (1.0 ml) at 60 ꢁC for 6 hours under
b
air. b Isolated cross-coupling yield.
air. Isolated cross-coupling yield.
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Table
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Pd-catalyzed desulfitative–denitrogenative Suzuki-type
(4-bromo-phenylsulfonohydrazide) under condition A, fol-
lowed by consecutive Suzuki cross-coupling by the simply addi-
tion of phenylboronic acid and H2O (0.5 ml, condition B),
provides the p-terphenyl (m-terphenyl) in the yield of 82% (84%).
This approach has great potential in combination of this trans-
formation to traditional Suzuki cross-coupling by the sequential
addition of water, without the demand for isolation of 4-bromo-
biphenyl(3-bromo-biphenyl) (Scheme 2).
coupling of arylsulfonyl hydrazides with arylboronic acidsab
The practicality of this Pd-catalyzed desultative–deni-
trogenative coupling reaction was further demonstrated by the
synthesis of 2-cyano-4-methylbiphenyl (OTBN, Scheme 3). This
biaryl compound is the key intermediate for the synthesis of
angiotensin receptor blocker (ARB) type antihypertensive
drug, such as candesartan cilexetil, valsartan and telmi-
sartan.14 The synthesis of AT2 antagonists represent one of the
most important industrial applications of Pd-catalyzed Suzuki
reaction. Our method provided a novel and effective route for
synthesis of OTBN intermediate. Aer further careful optimiza-
tion of our initial process, the coupling reaction of (2-cyanophenyl)
boronic acid and a slight excess of 4-methylbenzenesulfonohy-
drazide (1.05 equiv.) could be carried out very smoothly in 1
gramscale with 2.0 mol% of Pd catalyst and a lowered equivalent of
ligand. The yield of the crude product was almost quantitative. The
1H-NMR analysis of the crude products revealed that the purity of
the desired product was about 95% containing only a small
amount of the homocoupled product of boronic acid as an
impurity. The crude product can be used for the following trans-
formation without further purication.
a
Reaction conditions: arylsulfonohydrazide (0.5 mmol), arylboronic
A plausible catalytic cycle, as adapted from the mechanistic
studies performed on the Pd(II)-catalyzed desultative–deni-
trogenative coupling reactions of arylsulfonyl hydrazides,13 is
depicted in Scheme 4. Starting with the ligand coordinated
Pd(II)-complex, it is converted to Pd(II) species A and HOAc by
deprotonation with arylsulfonyl hydrazide. Next, (sulfonyldia-
acid (0.5 mmol), Pd(OAc)2 (5.0 mol%), Xantphos (10 mol%), K2CO3
b
(0.5 mmol), MTBE (1.0 ml) at 60 ꢁC for 6 hours under air. Isolated
cross-coupling yield.
Notably, amino group on the phenyl ring of boronic acids zenyl)PdOAc intermediate B is furnish by oxidation with
survived in the procedure (Table 3, 3h). Importantly, the desired molecular oxygen. Liberation of N2 with intermediate B gener-
product was formed in good yield when naphthalene was sub- ates the acetoxy(arylsulfonyl)palladium C, that form arylpalla-
jected to this procedure (Table 3, entries 3i and 3j). Good dium complex D by successive extrusion of sulfur dioxide.
coupling yield (95% and 88%) was still able to obtain when Transmetallation occurs with an arylboronic acid to affords the
coupled with heterocyclics, such as pyridinyl and imidazoyl diarylpalladium(II) species E. The reductive elimination
(Table 3, 3k and 3l). As expected, a series of functional groups provides the cross-coupling product and the active palladium(0)
on the phenyl ring of sulfonyl hydrazides, such as alkyl, alkoxy, species. Finally, Pd(II) species are then regenerated by the
nitro, uoro, chloro, bromo and cyano, were compatible under oxidation of the Pd(0) species with oxygen to close the cycle.
this procedure, and the products were isolated in good to
excellent yields (80–93%) (Table 3, 3m–3s). The m-, o-substitu-
tion didn't affect the reaction obviously and showed good
reactivity (Table 3, 3t and 3u). Notably, the iodo group is
extremely reactive in the Suzuki reaction, and its tolerance is
seldom reported in Pd-catalyzed cross-coupling reactions
(Table 3, 3v). Indolylsulfonyl hydrazides were efficiently coupled
with phenylboronic acid, no matter with methyl group on 1-
position or not (Table 3, 3x).
Another application of the presented desultative–deni-
trogenative coupling is its potential for combination with Pd-
catalyzed Suzuki–Miyaura cross-coupling to synthesize ter-
phenyl derivatives under “One-pot” process. The Pd- Scheme 2 “One-pot” synthesis of terphenyl.
catalyzed coupling of 4-bromo-phenylsulfonohydrazide
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hydrazides with arylboronic acids provides a versatile mean for
the construction of biaryl motifs. The methodology comple-
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